1. Field of the Invention
The present invention relates to, as one preferred example of application, a waveform simulation device for simulating an output waveform exhibited by a semiconductor device, more particularly relates to an input/output buffer information specification (IBIS) correction tool installed in the waveform simulation device etc. and an IBIS correction method.
2. Description of the Related Art
In recent years, LSIs and other semiconductor integrated circuits have been increasingly growing in circuit size. Simulators using computers are therefore becoming indispensable for their circuit design and circuit analysis. Among such simulators, the present invention particularly relates to a waveform simulation device for simulating the output waveforms of the basic components of semiconductor integrated circuits, that is, CMOS devices or other semiconductor devices as one preferred example of application. In further detail, an IBIS correction tool for correcting IBIS data provided from the outside of a modeling unit (explained later)—one of the principal components forming the waveform simulation device.
Note that as known art relating to the present invention, there is the Japanese Patent Publication (A) No. 2003-271692. An object of Japanese Patent Publication (A) No. 2003-271692 is, in the same way as the present invention, to obtain a desired precision in circuit simulation. In order to attain this object, this provides “simulation program with integrated circuit emphasis (SPICE) parameters used in circuit simulation of a semiconductor integrated circuit, wherein the SPICE parameters include sets of SPICE parameters divided for means using SPICE parameters expressing the entire range of a power supply voltage region and means using SPICE parameters expressing a low Vgs region of a gate-source voltage”. Japanese Patent Publication (A) No. 2003-271692 is different in configuration from the present invention explained later.
Regarding the IBIS data, this IBIS data is data expressing a so-called device model. This device model is usually comprised of data expressing an electrical characteristic of the output, that is, the voltage-current characteristic of the output, obtained by actual measurement or simulation for each semiconductor device. The output voltage-current characteristic data forming this device model is provided from for example the LSI manufacturer producing the semiconductor device.
In this case, that output voltage-current characteristic data is provided as data obtained under a certain specific power supply voltage as a representative voltage, that is, output voltage-current characteristic data corresponding to only one specific power supply voltage. This is because in recent semiconductor devices, the range of usable power supply voltage has grown greatly, so it has become difficult for the LSI manufacturer to provide the output voltage-current characteristic data under each power supply voltage over the entire range of the usable power supply voltage.
This being the case, a user requiring an output voltage-current characteristic under his desired power supply voltage (for example 2.8V) different from the above specific power supply voltage (for example 3.3V) cannot use the IBIS data for the specific power supply voltage provided for the semiconductor device as it is.
For this reason, conventionally, in the case of the above-described example, the user has simply shifted the provided output voltage-current characteristic curve by 0.5 (=3.3−2.8) V and used that as a substitute for the IBIS data for the desired power supply voltage (3.3V) (explained later with reference to the drawings).
However, when performing the simple voltage shift explained above for the above correction, there is the problem that, in part of the above-described output voltage-current characteristic, there is a part which ends up deviating from the output voltage-current characteristic obtained by actual measurement or simulation. Error occurs there, so corrected IBIS data corresponding to the above-described desired power supply voltage cannot be obtained with a high precision.
In this case, it is also naturally possible to extract the output voltage-current characteristic data per se for that desired power supply voltage by actual measurement or simulation. However, enormous time and cost are required for such actual measurement or simulation, so this is not realistic.